ORTFIOCERAS. I33 



spaces, corresponding in number with the septa, and becoming more and more 

 obscure towards the summit of the shell. Both rings and interspaces crossed by- 

 numerous, distant, rounded, longitudinal threads, between which is a second series 

 of much less prominent lines. 



Size. — The largest specimen known, though wanting both the body-cbamber 

 and the apical portion, measures 153 mm. in length. Its diameters at the summit 

 (which may be slightly compressed) measure respectively 32 mm. and 26 mm. 



Locality. — Wolborough. There is a fine, though worn, specimen of the aged 

 shell, as well as two other fragments which agree with it, in Mr. Vicary's Collection. 

 In the Torquay Museum is another fine and beautifully marked example, which 

 has more prominent ribs than the former, and this comes nearer to 0. tubicinella, 

 as well as a fragment of the body-chamber, in which the rings are shown to be almost 

 obliterated. In the Museum of Practical Geology are two fragmentary specimens, 

 which respectively correspond in ornamentation to the two last mentioned. 



BemarJcs. — The fine and aged shell in Mr. Vicary's Collection, which is the type 

 of this species or variety, was identified by Salter with 0. ludense, Sow.^ With 

 that species, however, it has certainly no afiinity. Neither is it at all similar to 0. 

 striatulmn, Sow.,^ which is a far more conical form. There appeared no reason 

 at first for imagining it to be at all connected with 0. tubicinella, from which it 

 presents numerous differences ; but on comparing it with the above-mentioned 

 specimen from the Torquay Museum and with the numerous specimens of 0. tubici- 

 nella which will be noticed below, its relationship comes out. Though Mr. Vicary's 

 shell differs much from the Torquay specimen, its lower portion is so worn that the 

 nature of its markings cannot be made out, and at the upper extremity of the latter 

 there appears to be a change of ornamentation, leading to the supposition that if 

 more of the upper part had been preserved it would have shown similar features. 

 The specimen of the body-chamber shows that these characters are even more 

 developed in that part, the rings having almost entirely disappeared. For this 

 reason I have placed it under this head, but it is quite possible that in 0. 

 tubicinella itself the rings may be obliterated on the body-chamber. 



Owing to the great amount of variation in the specimens of these two species 

 and of 0. sub-tubicinella, and their fragmentary condition, it has been very difficult 

 to decide whether they really are distinct forms, or simply belong to one largo 

 and very variable species ; at times I have been much inclined to group them 

 together, but, after repeated examinations and consultations, it has seemed best 

 to regard them as three distinct forms. As far as can be judged by the specimens 

 examined, which, though fine, are all more or less fragmentary, there appear to be 

 certain definite distinctions between them, and it only remains to see whether 



1 1839, Sowerby, Murch. ' Sil. Syst.,' p. 619, pi. ix, figs. la,lh. 



2 1840, Ibid., ' Geol. Traas.,' ser. 2, vol. v, pt. 3, p. 703* pi. liv, fig. 20. 



